This study entails the development and methodology of use of pulsed carbon dioxide laser systems, pulsed Nd:YAG laser coupled to a slit lamp, Q-switched Excimer lasers, and high-power CW Argon laser with fiber-optic delivery systems. For the CO2 and Nd:YAG laser systems systematic studies of animal vitrectomies were performed in order to characterize laser pulse characteristics necessary to transect vitreal membranes. Additional studies of retinal damage as a function of pulse characteristics and distance of cutting site from the retina clarified the potential for use of these laser systems close to the retina. For all laser systems systematic studies of tissue damage on human coronary arteries was performed so as to determine their feasibility (and optimal system design) for laser angioplasty. The Argon laser/fiber optic system was able to ablate artery wall and non-calcified plaque when probe was kept in contact with the bottom of the crater as it was formed. Argon laser systems could not ablate calcified lesions. High power nanosecond (or shorter) duration Nd:YAG laser pulses could easily remove noncalcified plaque but removed calcified plaque only very slowly. Additionally large fissures in the artery wall occured, most likely the result of shock waves created by the transient absorption of the laser energy. Submillisecond CO2 laser pulses ablated tissue with minimal thermal damage to surrounding tissue. Excimer laser pulses etched very clean craters in calcified as well as non-calcified plaque. Evaluation of prototype fiber-optic laser angioscopes in animals were carried out to evaluate this technology as an adjunct to surgery and as an aid in directing laser angioplasty. Human fibr-optic angioscopy during bypass surgery has been initiated.